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Past Events & Hot Topics - 80% drop in atmospheric CO2

USING crowdfunding to raise money for science neglected by conventional grant-giving agencies is all the rage. Indeed, there is almost a return to a lost era of amateur natural philosophers and natural historians—with the twist that the amateurs merely stump up the cash, rather than doing the actual research. It seems appropriate, therefore, that one of the latest projects to go down this route would probably have tickled the fancy of many a Victorian gentleman naturalist with a taste for unusual plants in his conservatory. It is an investigation of ferns.

Though it is hard, as the price of DNA sequencing has plummeted, to believe that there is any important group of organisms which has not had the genome of at least one representative species scrutinised, Kathleen Pryer of Duke University, in North Carolina, claims this is true of ferns. She proposes to correct that by looking at an unusual member of the group, using money raised on experiment.com, a crowdfunding site that exists to support scientific research.

Azolla (pictured) hardly looks like a typical fern and, as an aquatic rather than a terrestrial plant, does not behave much like one either. But it is probably the most economically important fern on the planet—and it may also once have been responsible for changing the climate.

Azolla’s significance comes from its partnership with several species of bacteria that can manage a trick no plant finds possible by itself: extracting nitrogen from the air and “fixing” it into chemicals such as ammonia, so that it is available to make proteins. Asian rice farmers have known of Azolla’s fertilising properties for at least 1,500 years, and in many places the fern is encouraged to grow alongside rice in paddies—a sort of aquatic version of alfalfa. Dr Pryer’s primary pitch, therefore, is that understanding the genomes of Azolla and its associated bacteria (which she proposes to sequence at the same time) might assist the improvement of this process, and maybe aid its transfer to other plants.

She would also, though, like to know more about the genetics behind the “Azolla event” of 49m years ago—a giant bloom of her beloved fern that coincided with one of the biggest climate shifts known. The surface sea temperature in the Arctic, for example, dropped from 13°C to -9°C and many, including Dr Pryer, think the coincidence was, as it were, no coincidence. Rather, Azolla was the cause.

What is indisputable is that a lot of Azolla is buried in polar rocks from this epoch, the mid Eocene. The reason seems to be that continental drift at that time formed a polar ocean even more cut off from the rest of the sea than today’s Arctic Ocean is. The result was something akin to a giant version of the Black Sea—with a fresh surface layer fed by rivers from the surrounding land, and a bottom so stagnant that anything falling to it would not rot. The surface layer would have been perfect for Azolla to live in, and the bottom perfect for preserving it when it died and sank. And the fern’s ability to fix nitrogen, together with the long, sunny days of polar summers, mean it would have grown like billy-o, as the fossil record shows it did.

Calculations suggest that a mere 800,000 years of this process of forming and buryingAzolla, along with all the carbon it had sucked out of the atmosphere as it grew, would have been enough to account for the 80% drop in atmospheric CO2 that other rocks suggest happened during the mid Eocene. This, by greatly reducing the greenhouse effect, cooled the Earth from temperatures in which palm trees grew at the poles to the sort that are experienced today.

Much of the Azolla which sank then still remains buried, and with it the Earth-warming carbon it contains. But that carbon has been transformed over the millennia. A good proportion is now oil and gas. And many people are interested in drilling in the Arctic to extract these fossil fuels, burn them and return the carbon to the atmosphere—there, perhaps, to reverse the events of 49m years ago.

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